1. Field of the Invention
The invention relates generally to electrically driven centrifugal submersible well pumps, and in particular to an oil and water separator for separating oil from the well fluid prior to reaching the pump for the purpose of selectively directing oil or water flow into intimate contact with the electric motor.
2. Description of the Related Art
The application of ESPs to viscous crude has been increasing in recent years. Today ESPs are applied to heavy crude production where pumping viscosities can exceed 1000 centipoise. At these viscosities, there are considerable losses associated with ingesting viscous crude within the pump and additional losses experienced in discharge head and efficiency of the pump due to the viscosity. These losses limit the flow rate, therefore limiting the amount of crude produced. These losses also cause severe reduction in the head/stage ratio, thereby requiring a significantly larger pump. Furthermore, the losses cause an increase in the horsepower required to produce the crude, resulting in larger equipment and significant increases in power costs.
A different problem arises in situations where the well fluid entering the well machinery in the well assembly has high temperatures. In this situation, the motor powering the pump experiences temperature problems because the high temperature well fluid passing the motor will not collect the heat from the motor. Therefore, the motor has no way to transfer its heat to the well fluid passing by the motor.
The system for treating and pumping well fluids of this invention has a downhole motor connected to and below the pump. A shroud encloses a substantial portion of the motor. A separator below the shroud separates the oil and liquid from the well fluid. One of the oil outlets of the separator communicates with the interior of the shroud and the other outlet discharges to the exterior of the shroud. The liquid oil and water recombine before entering the pump.
The shroud prevents the separated oil and water from mixing. In one embodiment, openings in the shroud above the motor allow the water to enter inside the shroud and recombine with the oil before entering the pump. The oil flowing past the motor has a lower thermal conductivity than the water on the exterior of the shroud. The heat generated by the motor lowers the viscosity of the oil.
The separator may be a hydroclone having a conical separation chamber that uses gravity and centrifugal forces to separate the water and oil from the well fluid. Alternatively, the separator may also be a centrifugal separator, having at least one impeller blade and at least one vane, the blades and vanes shearing through the fluid to create centrifugal forces which separate the water from the oil.
Another embodiment is used in the situation where the temperature of the well fluid entering the well prevents the transfer of heat from the motor to the well fluid. In this embodiment, the separator directs the oil to the outside of the shroud and the water to the inside of the shroud. The water from the well fluid is more receptive to receiving the heat from the motor than oil because of a higher thermal conductivity. Therefore, the water in intimate contact with the motor cools the motor while the water flows passes by the motor.